Many database management systems are available to help users manage data. One way such systems help users is to answer questions the users have about the data. In the context of database management systems, questions are typically referred to as “queries” and answers typically referred to as “results”. Users submit queries to database management systems and receive answers to the queries in the form of results.
To answer queries, database management systems use computing resources such as memory and processor resources. Different queries require different amounts of computing resources to answer. For example, a query that returns 50,000 results may consume more computing resources than one that returns 10 results.
Many database management systems have the ability to execute multiple queries at the same time (i.e., concurrently). The process performed by a database management system of determining the results of a query is often referred to as “executing” the query. Multiple queries executed concurrently by a database management system can contend with each other for use of the same computing resources. Many database management systems perform synchronization and scheduling functions for the purpose of sharing computing resources amongst multiple concurrent query executions.
Unfortunately, despite these synchronization and scheduling efforts, problems can arise when database management systems execute multiple queries concurrently where some of the queries are “high cost” queries and others are “low cost” queries. With this type of mixed query-load, execution of the high cost queries can require use of so many computing resources that they “starve” low cost queries of computing resources. The result may be that the database management systems take a long amount of time to return answers to the low cost queries. Overall, some database management systems handle mixed query loads in such a way that latency of the low cost queries and the throughput of the query load are longer than users expect them to be.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.